The invention generally relates to electronic devices, and more particularly to buck converters.
Buck converters are used to convert a higher voltage to a lower voltage suitable for use by, for example, a microprocessor. A conventional buck converter is disclosed in U.S. Pat. No. 6,166,528, issued to Rossetti et al. on Dec. 26, 2000, the disclosures of which are hereby incorporated by reference. Typically, a buck converter operates using a clock, whereby an inductor is charged during a first portion of a clock cycle (xe2x80x9ccharging phasexe2x80x9d) and operates as a current source during the second portion of the clock cycle (xe2x80x9cdischarging phasexe2x80x9d).
FIG. 1A, shows a typical buck converter 10, which includes transistors 14 and 18, a controller 20, an inductor 24 and a capacitor 28. Buck converter 10 operates by commencing the charging phase in response to a clock signal. During the charging phase, inductor 24, capacitor 28 and a load (not shown) connected at the output voltage Vout are coupled to an input voltage Vin. Meanwhile, the inductor current iL is monitored by controller 20. When iL peaks at a predetermined value, converter 10 is decoupled from the input voltage Vin and inductor 24 discharges its energy through the and capacitor 28. The inductor current iL rises and falls linearly with slope of diL/dt=(VL/L), where VL is the voltage across the inductor. FIG. 1B shows Vin and iL signals in buck converter 10.
When there is a rapid reduction in load current demand, controller 20 simply waits while the current in inductor 24 discharges into capacitor 28 and the remaining load causing a rapid increase in the output voltage Vout. For example, microprocessors, such as Pentium(copyright) and Itanium(copyright) require voltages near 1.5 V and currents near 60 A and the current changes from 0 to 60 A and back in nanoseconds. Such an increase in Vout can result in serious damage to capacitor 28 and/or the load. Therefore, the capacitor must have a very large value to limit the voltage rise to a xe2x80x9csafexe2x80x9d amount during such a rapid current surge. Capacitors with large values, however, are much more expensive and are among the most expensive components in a buck converter. This increases the overall cost of a buck converter.
Therefore, there is a need for a low cost buck converter without degrading its performance.
The present invention provides a low cost buck converter without compromising the performance. According to an embodiment of the invention, a buck converter comprises an input circuit for receiving an input signal, a controller connected to the input circuit for controlling the input circuit, a switch controllable by the controller for switching on/off, a current storage element connected to the input circuit and connected in parallel with the switch, and an output voltage storage element, connected to the current storage element, for connecting in parallel with a load.
According to one aspect of the embodiment of the invention, in a charging phase, the controller causes the input circuit to allow the input signal to pass through and be provided to a load via the current storage element. The controller also causes the switch to switch off and become an open circuit.
According to another aspect of the embodiment of the invention, in a discharging phase, the controller causes the input circuit to decouple from the input signal and causes the switch to switch on and become a short circuit, so that current flows within a loop formed by the switch and the current storage element.
According to a further aspect of the embodiment of the invention, the discharging phase occurs when the controller detects a rapid decrease in a load current flowing into the load. The discharging phase also occurs when the controller detects an over voltage condition at the output voltage storage element.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.